Apparently, after shooting a new epsidoe of 7th Heaven, Mackenzie was riding one of her horses and fell off after her horse was startled by something. She was hospitalized and has a broken arm and sprained wrist. This happened Friday.

I got the information from tvtome.com

Here is what it says at tvtome:

MacKenzie Rosman was injured yesterday after falling from her horse at her ranch. The accident happend when MacKenzie went for a horseback ride in the woods near her house. Allegedly she fell from her horse after the horse was frightened by something. MacKenzie was admitted to the hospital with a broken arm and a sprained wrist, as well as a possible concussion.

They added the thing about the concussion today.

:( I Hope shes Ok.

oh my god...!

I hope it's not too serious...

Oh, no! :( She's one of my favorite actresses!!
I hope she's ok!!

I wonder if they'll say anything about it on the show.